Aircraft: B737
Phase of flight: Descent
Anomaly: Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Inflight Event / Encounter Bird / Animal

It was VFR night time on approach. We briefed the visual approach backed up with the ILS. I had just slowed to about 230 knots as we were about seven miles from the FAF and I knew a descent was coming. ATC gave us a descent from 4000 FT to 2000 FT. At approximately 3500 FT we hit a flock of birds. I heard and felt multiple impacts. A rancid odor filled the cabin. I also saw a bird pass by my right side and my first thought was it may have gone in the #2 engine. I immediately looked at the engine parameters for both engines but noticed no change or abnormal indication. The only abnormal indication was the illumination of the Forward Leading Edge in Transit light accompanied by a yellow Overhead Left Wing flap in transit light. The Captain told ATC we hit multiple birds and needed to verify the aircraft configuration before continuing the approach and asked for a vector off final approach to run through the Flap Leading Edge in Transit QRH Checklist. Before running the checklist; the Captain called the Flight Attendants and informed them we hit birds and he would get back to them after we knew our status. While the Captain was talking to the Flight Attendants and turning a downwind; the aircraft started to vibrate. I looked at the VIB display and Number 1 showed 0.1 and Number 2 showed 0.4. I did see the Number 2 engine N1 fall about 15% lower than the Number 1 engine; but the autothrottles pushed it back up to match the Number 1 N1. I reduced the power on the Number 2 engine and the vibration stopped. At some point the autothrottles automatically disengaged. The Captain finished talking to the Flight Attendants and informed me that they reported that the Number 2 engine was on fire. There were no cockpit indications of a fire. The Captain advised ATC we needed to return to the field and have the fire trucks standing by. He also took control of the aircraft and became the Pilot Flying. We decided that the report of the fire and our proximity to the airport made getting on the ground a priority. The Captain asked for landing gear and flaps to start slowing down. The aircraft handled symmetrically so Forward Leading Edge in Transit light was not a concern when compared to getting on the ground. While we were on about a seven-mile final; the Flight Attendants informed me that the fire was out and to see if we could make a PA because the Passengers were upset. I made an announcement that we hit some birds and would be making a normal landing shortly. I did not inform the Captain that I made that PA so he ended up making the same announcement about 30 seconds later. Due to the Forward Leading Edge in Transit light; we decided to land flaps 15. The Captain had me run the numbers for a flaps 15 landing. We had the stopping margin and used auto brakes max. In the short time before touchdown; we ran through the Forward Leading Edge in Transit light QRH Landing Checklist. After touchdown; we cleared the runway and we did after landing flow without changing the configuration of the aircraft. We still had no cockpit indications of a fire. I talked to the Fire Chief to have him see if any fire was observed. The Captain talked to the Flight Attendants to update them on our situation. No evacuation planned at this point. ARFF indicated there was no fire upon inspection and we taxied to gate and deplaned normally. We ran the Shutdown Checklist and made a logbook entry. There were no reported injuries to the Passengers or Crew.The number of people that want your story immediately after an event is understandable. However; it is difficult to tell your story so many times to different people minutes after the incident. It would be helpful to take some time to wait for our reports or to get the story out to one person and have them be a liaison for others wishing to hear the events. Multiple bird strikes causing Leading Edge Flap light and engine vibration/fire. We briefed the Visual Approach; backed up with the ILS and ATC gave us a descent from 4000 FT to 2000 FT with a vector towards the airport. At approximately 3500 FT; we encountered a flock of birds. I heard and felt multiple impacts. We first notice the Forward Leading Edge in Transit light accompanied by a yellow Overhead Left Wing Flap in Transit light. I told ATC we hit multiple birds and needed to verify the aircraft configuration before continuing the approach; and asked for a vector off final approach to run through the Flap Leading Edge in Transit Checklist. Before running the checklist; I called the Flight Attendants and informed them we hit birds and I would get back to them after we knew our status. After we turned away and started to work the checklist; we got a call from the Flight Attendants informing us the #2 engine was on fire. There were no cockpit indications of a fire. The First Officer observed a reduction in #2 engine N1. We both felt the vibration; the First Officer further reduced the power in the #2 engine and the vibration stopped. I declared an emergency and advised ATC we needed to return to the field and have the fire trucks standing by. We transferred aircraft control and I was the Pilot Flying. The aircraft handled symmetrically. We agreed we needed to land immediately. We got a descent to 2000 FT and took clearance for the visual. The Flight Attendants called to say the fire was out.We decided to land flaps 15. We ran the QRH for a flaps 15 landing. We had the stopping margin and used auto brakes max. We did a PA to tell the Passengers and Flight Attendants that we had hit birds; but the aircraft was flying fine; and we would land in three minutes; and it would be a normal landing. After touchdown; we still had no cockpit indications of a fire. The First Officer talked to the Fire Chief to have him see if any fire was observed. I talked to the Flight Attendants to update them on our situation. No evacuation planned at this point. ARFF indicated there was no fire upon inspection; and we taxied to gate and deplaned normally. We ran the Shutdown Checklist and made a logbook entry.Do do not ask Crew Members if they can continue on; just pull them; they are not capable to make that call under the circumstances. We hit a big flock of big birds. B737-700 flight crew encounters a flock of birds at 3;500 feet during a night visual approach. The crew felt multiple impacts and a Forward Leading Edge in Transit light illuminated. Vibration is felt and indicated on the number two engine and flight attendants report the engine is on fire. When thrust is reduced on the right engine the vibration stops and the flight attendants report the fire is out; although no fire was ever indicated in the cockpit. A flaps 15 approach and landing ensues.